Carbon Quantum Dot from Areca Husk as an efficient Photosynthetic Enhancer for Sustainable Agriculture

doi:10.21203/rs.3.rs-4652210/v1

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Carbon Quantum Dot from Areca Husk as an efficient Photosynthetic Enhancer for Sustainable Agriculture

https://doi.org/10.21203/rs.3.rs-4652210/v1

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Carbon Quantum dots (CQDs) are nanostructured materials that have gained immense application in the field of agriculture. They have unique properties because of their less toxicity and environmental stability be it as a growth enhancer or as an antibiotic. The synthesis of carbon quantum dots from areca husk here, exemplifies a novel approach, offering environmentally friendly and less toxic nanomaterials that may revolutionize agricultural practices. This work highlights synthesis of carbon quantum dots from areca husk using hydrothermal method. In this study, characterization through UV spectroscopy clearly indicated the fluroscent property of the syntheised CQDs. FTIR characterization showed the presence of the CO(carbonyl) and OH (Hydroxyl) groups present and emphazising on the antimicrobial property of CQDS. XRD analyses highlighted that 97.5% of the sample had crystalline structure and 2.5% was amorphous. CQDs treated seeds showed healthy seedling growth with 7.682mg/g of cholorophyll content being highest in corn whereas11.42mg/g in wheat compared to other treatments emphasising the increase in photosynthetic efficiency. The integration of CQDs presents a promising avenue for revolutionizing modern agriculture towards greater sustainability and potential for improved yield.

Areca husk

Carbon quantum dots

Characterization

hydrothermal method

UNSDGs 2

Zero Hunger

The world arecanut production in 2020 was 17.96 lakh tonnes from an area of 12.26 lakh hectares with an average yield level of 1.46 tonnes/ha. Over the years, both global area and production of arecanut exhibited increasing trends. (https://ccari.icar.gov.in/ExtensionFolder No.107.pdf). A significant portion of this waste is disposed of through burning, leading to the unfortunate loss of a potential organic resource and valuable plant nutrients. The accumulation of areca husk in plantations results in unpleasant odors, decay-related issues, and contributes to environmental pollution. However, this husk possesses the potential to be a valuable raw material and converted into value added products [Vasudeva Nayaka et al., 2019 ].

Quantum dots often referred to as "artificial atoms," represents nanostructured materials that have garnered significant attention owing to their distinctive properties spanning optics and electronics. These optically steadfast and innovative fluorophores exhibit a broad spectrum of applications from medical to agricultural domains, holding vast potential to revolutionize various industrial sectors [Gupta, A et al.,2022]. Carbon quntum Dots are known for their desirable qualities, including ultra-small and uniform size, low toxicity, biocompatibility, high water solubility, affordability, chemical inertness, eco-friendliness,adjustable photoluminescence and simple cell penetration. They also have a significant potential for use in agriculture applications[Lim, S. et al.,2015]. Photosynthetic enhancers are of recent study in agriculture. Photosynthesis help plants transform solar energy into chemical energy. But less than 10% of sunlight is used by chloroplasts and they can only use it in the visible spectral range (400–700 nm), primarily in the blue and red. Plant photosynthesis does not use UV or nIR light sources. However, the fact that CQDs are engaged in the process of turning dangerous UV radiation into harmless photosynthetically active radiation without any appreciable energy transfer, suggests that UV light may be used safely in photosynthesis when combined with QDs[Li.Y. et al.,2020]. Though there are studies of the effect of C dots on seed germination the precursors used for the synthesis of C dots are inorganic and have many toxic effects once treated [Liang, Let al., 2023., Liang, Z.,2021, Babu,S.,2022, Wang, Y.,2021]. Therefore, this current study involves the synthesis of carbon dots using organic agricultural waste and investigates their impact on the germination and growth of seeds, namely corn and wheat. The overarching goal is to contribute to a zero-waste cycle and promote sustainability.

Collection and treatment of Areca husk

Areca husk was collected from Davanagere, Karnataka, India and sun-dried. This preliminary step aimed to eliminate moisture and prepare the husk for subsequent processing. 3 kilograms of husk,

with grinding process in a mixer resulted in approximately 70 grams of finely powdered husk Finely powdered husk was taken for the synthesis of carbon quantum dots. The hydrothermal synthesis method has been widely employed to create carbon quantum dots (CQDs). Typically, the sizes of these CQDs are regulated through the manipulation of precursor concentrations, processing temperatures, and reaction durations [Nammahachak, N. et al.,2022].

Synthesis of carbon quantum dot:

Areca husk (70g) was grinded with 400ml of distilled water in mortar and pestle to get extract solution. Extract solution was centrifuged at 10000rpm for 15min and supernatant was collected. The extract solution was heated in magnetic stirrer at 150°C for 1hr and dark product obtained was dissolved in 20ml of water. Residue was subjected to filtration and 50ml of ethanol was added to it. Centrifugation at 10000rpm for 15 minutes, Separated the supernatant and pellet. 20ml of pellet was dissolved in 1N NaOH to stabilize the solution. Solution was kept at room temperature for 48h to extract high fluorescent quantum dots.

Characterization of synthesized CQD

CQDs were characterized using UV spectroscopy, FTIR and XRD [Rooj B. and Mandal,U., 2023., Tungare, K.,2020, Azam, N et al., 2021, ]

UV-visible spectroscopy is a commonly used technique for the characterization of carbon quantum dots (CQDs). This method involves UV and visible light onto the CQDs and measuring the absorption and reflection of light at various wavelengths [Rooj B. and Mandal,U., 2023.,].

FTIR analysis: FTIR spectroscopy is utilized to identify chemical bonds, assess molecular composition, ensure material quality, and aid research across industries and scientific fields. The following peaks represents various bonds at 3200–3600 cm^-1: Hydroxyl (OH) groups. Peaks at 1600–1750 cm^-1: Carbonyl (C = O) groups. Peaks at 1600–1680 cm^-1: Carbon-carbon double bonds (C = C).Peaks at 2800–3000 cm^-1: Carbon-hydrogen (C-H) bonds. Peaks at 1000–1300 cm^-1: Ethers, alcohols, or carboxylic acids (C-O)[ Tungare, K.,2020].

X-ray diffraction (XRD)

In X-ray diffraction (XRD), the primary parameter obtained is the diffraction pattern, which consists of the diffraction peaks and their associated intensities. These peaks provide valuable information about the crystal structure and lattice properties of the sample being analyzed [Azam, N et al., 2021].

The size of the quantum dots < 2 nm emits blue fluorescence, 2–5 nm emits green color, 5–8 nm emits yellow color, 8-10nm emits orange color and > 10 emits red florescence (DOI: 10.5772/intechopen.71428).

Assessment of CQD for photosynthetic enhancer:

Untreated wheat and corn seeds were collected directly from the farmers field from shimoga district, Karnataka, India. The study was carried out in accordance with relevant guidelines and regulations of RV College of Engineering.These wheat and corn seeds were germinated in germination tray/netted pots of 2’’ size and one seed per pot as control, synthetic seed treatment, and CQD treatment. Here depicted as CW/CC = control wheat/control corn, SST = synthetic seed treatment and CQD = carbon quantum dot. 63 seeds were sown in three replications R1 R2 & R3.Complete randomized Design (CRD) was adopted. The plants were monitored daily for the growth. Swabbing method was adopted for CQD treatment and later the leaves were checked for chlorophyll content.

Swab method

Sterilized cotton was dipped in CQD solution and swabed up and below the leaf surface of wheat and corn seedlings.The swabbing was repeated after every 3 days interval.Observations were recorded and photographed on 4th, 8th 12th and 16th day of germination.

Chlorophyll extraction: The study was carried out in accordance with relevant guidelines and regulations of RV College of Engineering. 1g of leaves of wheat and corn seedlings were grinded in 20ml of 80% chilled acetone in pestle and mortar.The residue was transferred to vial and centrifuged for 5min at 5000rpm. Supernatant was collected and 20ml of 80% chilled acetone was added and again centrifuged for 10mins at 5000rpm. Supernatant was collected and diluted in 1:3 ratio. The absorbance was measured at 645, 652, 663nm using UV spectrophotometer. Formula for calculating chlorophyll content is as follows:

Chlorophyll A = (12.7 * A663–2.69 * A652) * V𝑊

Chlorophyll B = (22.9 * A652–4.68 * A645) * V𝑊

Total chlorophyll = Chlorophyll A + chlorophyll B

Statistical Analysis

The statistical analysis was done using p-value approach for testing our hypothesis. The lower the p-value, the greater the statistical significance of the observed difference. p-value of 0.05 or lower is generally considered statistically significant and above is generally considered non-significant.

Synthesis of CQD:

The synthesised CQD exhibited notable green fluorescence using the hydrothermal method at a controlled temperature of 150 degrees Celsius. The resultant mixture was subjected to filteration using the dialysis memberane (70) to obtain a clear solution, which was then left at room temperature for a period of 48 hours. Notably, a significant yield of high-quality Carbon Quantum Dots (CQD) was observed in the liquid supernatant (shown in below figure 1a to 1b) while not observed in pellet.

Characterization:UV spectroscopy characterization:

CQDs typically shows strong absorption in the UV region (200-400 nm). Peaks at specific wavelengths indicate the presence of chromophores in sample. Different chromophores absorb light at different wavelengths, so the presence of peaks at 244 nm and 294 nm suggests the existence of distinct chromophores absorbing light at these wavelengths. The position and intensity of these peaks provide information about the energy levels within the CQDs.

FTIR analysis:

In fig.2 two peaks were found in FTIR results, indicating the presence of two different functional groups in the sample. Each peak corresponds to a distinct functional group. The observed peak is 1634 cm^-1 and another peak around 3332.62 cm^-1, suggests the presence of both a carbonyl group (C=O) and hydroxyl group (O-H) in the sample.

From literature survey in terms of antimicrobial property OH group is significant and it possess properties that can inhibit the growth and survival of microorganisms by disrupting cell membranes, inhibiting enzyme activity or interfering with cellular processes. So, the above result shows that its having hydroxyl group and hence its potential of having antimicrobial property.

X-ray Diffraction:

XRD result of CQDs

The X-ray diffraction (XRD) analysis of carbon quantum dots (CQDs) has revealed the presence of distinct peaks, indicating the existence of a crystalline structure within the CQDs. The intensity of these peaks is correlated with the concentration of the crystalline phase, with stronger and sharper peaks denoting a higher degree of crystallinity(97.5%) and amporhous (2.5%). These results are in contradictory to the results of CQD syntheised using plastics wherein the samples was amporphous in nature (100%) when analyzed in XRD [Liang, L., 2023 ]

CQDs as Photosynthetic Enhancer:

Soil germination of Corn: On the 4^th, 8^th,12^th and 16th day of germination, there was a notable difference in the growth of three groups: the control, synthetic seed treatment, and CQD-treated corn. As evident from the figure 3a, notably, the corn treated with CQDs exhibited significantly faster germination compared to the other two groups. This highlights the accelerated germination effect of CQDs, setting them apart as a potent enhancer of early corn growth.Similar results were quoted by Chauhan P. et. al.,2022 who quoted the same results in Seed germination studies on Chickpeas, Barley, Mung beans and Wheat with natural biomass and plastic waste derived C-dots.

Soil germination of wheat:

Seeds sown in soil as control,synthetic seed treatment was poor when compared to the remarkable growth observed in seeds treated with carbon quantum dots (CQDs). As evident from the figure 3b notably, as the germination progressed beyond the 8th day, a concerning trend emerged, the seedlings from the control and synthetic seed treatment groups displayed signs of declining health and vigor. This underscores the potential and positive impact of CQDs in fostering robust and sustained seedling growth, setting them apart as a promising treatment option for enhanced germination and plant development. Similar results were observed by Chauhan P.et. al.,2022 in Chickpeas, Barley, Mung beans and Wheat seed germination studies.

Anova table for 4^th, 8^th,12^th and 16^th day of Corn and Wheat germination

Statistical analysis of the germination of seeds and its growth was conducted. On the 3rd day, the germination data showed statistically significant differences among the groups. (Tables not shown) However, on the 6th, 9th, and 12th day, some of the data did not show statistical significance due to concurrent readings. This suggests that the differences between groups might not have been strong enough to be considered statistically significant. Despite the statistical nonsignificance, it is noted that the plants treated with carbon quantum dots appeared to be healthier compared to the other groups. This was further confirmed with the chlorophyll quantification.

Chlorophyll Quantification in Corn and Wheat

Table 1a: Chlorophyll content of Corn
Wavelength (nm)	Absorbance
	Control	Synthetic seed treatment	CQD
645	0.183	0.144	0.200
663	0.275	0.217	0.299
652	0.495	0.392	0.542
Total Chlorophyll (mg/g)	10.48	8.27	11.42
Table 1b: Chlorophyll content of Wheat
645	0	0.053	0.131
663	0	0.149	0.198
652	0	0.082	0.363
Total Chlorophyll (mg/g)	0	3.79	7.682

In Table 1a, the control group is listed as zero. In contrast, the synthetic seed treatment yielded a chlorophyll content of 3.79 mg/g, while the CQD-treated group displayed a significantly higher chlorophyll extraction of 7.68 mg/g. Among all treatments, the CQD treatment clearly stands out with the highest chlorophyll content, indicative of its role as a photosynthetic enhancer. Similarly, in Table 1b which records the chlorophyll extraction for wheat, the control group exhibited a chlorophyll content of 10.48 mg/g, the synthetic seed treatment resulted in 8.27 mg/g, and the CQD treatment showed the highest chlorophyll content at 11.42 mg/g. The CQD treatment surpasses the other treatments, affirming its capacity as a photosynthetic enhancer. These results underscore the valuable role of CQDs in promoting chlorophyll production and consequently enhancing the photosynthetic capabilities of both corn and wheat.

Carbon quantum dots (CQDs) synthesized using innovative green synthesis approach not only effectively repurposes agricultural waste but also yields CQDs with remarkable properties.Their multifaceted benefits encompass improved germination, enhanced early-stage growth, and increased photosynthetic efficiency, all of which collectively contribute to a more resilient and productive agricultural system. However a detailed work both in lab and field conditions needs to be done for taking the technology forward for commercialization.

CQD- Carbon Quntum Dots, UV- Ultra Violet spectroscopy,FTIR – Fourier transform Infrared spectroscopy, XRD – X ray diffraction, UNSDG-(United Nations Sustainability Development Goals.

Acknowledgement: I sincerely thank Principal, RVCE for providing the necessary support and encouragement

Data Availability Statement :The data supporting this article have been included as part of the Supplementary Information.

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No competing interests reported.

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Carbon Quantum Dot from Areca Husk as an efficient Photosynthetic Enhancer for Sustainable Agriculture

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Abstract

Figures

Introduction

Methodology

Collection and treatment of Areca husk

Synthesis of carbon quantum dot:

Characterization of synthesized CQD

Assessment of CQD for photosynthetic enhancer:

Results and Discussion

Conclusion

Abbreviations

Declarations

References

Additional Declarations

Supplementary Files

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